Assessment of Root Morphology and Apices of First and Second Maxillary Molars in Tehran Population

Introduction

The main goal of root canal therapy (RCT) is to biomechanically clean the pulp chamber and root canals and prepare the root canal system for obturation; RCT must achieve a three-dimensional seal at the apical and coronal regions and prevent any connection between the internal root canal system and the surrounding periodontal tissues (1). Inadequate cleaning and shaping of the apical region often results in remaining contaminated tissue residues and necrotic debris in the canal. Presence of these stimulants at the apical region can cause persistent periapical inflammation and subsequent root canal treatment failure (1). Radiography is a diagnostic tool in endodontic treatment. However, due to its two-dimensional nature, it has many limitations. Thus, knowledge as to the number and morphological variations of the root canals and the odds of extra canals being present can help achieve higher treatment success.

The roots of some teeth, especially the mesiobuccal (MB) root of maxillary molars, distal root of mandibular molars and to a lesser extent, the maxillary first premolar and mandibular anterior teeth have two canals (2-7). Vertucci classified root canals in 8 groups (Figure 1) (1, 8(

Figure 1.Vertucci’s classification of root canal systems (1, 8)

To date, several studies have evaluated tooth apices. Multiple foramina, apical delta, apical isthmus and accessory canals have been frequently reported in the apical one-third of teeth. Such variations can complicate the process of cleaning and shaping of root canal systems (1). Apical delta is defined as the division of the main canal and presence of multiple apical foramina at the apical region (9).

In normal root canals, the most apical part of the canal narrows and forms the apical constriction (1). The canal then widens from this point on and is referred to as the main apical foramen (10). The main apical foramen does not usually correspond to the anatomic apex and is laterally deviated in such way that it is often located 0.5 to 2 mm coronal to the anatomic apex (1(.

In a study by Green et al, almost 50% of main foramina directly opened to the apex and the amount of deviation from the apex was reported to be up to 2mm (11). Kuttler et al, in their study on two age groups of 18-25 yrs. and 55 yrs. reported that in 32% and 20% of cases, apical foramina did not deviate from the anatomic apex, respectively. The mean distance of apical foramina from the anatomic apices was 495 microns in the first and 607 microns in the second age group (12, 13). This study aimed to assess the possible variations in root canal anatomy and topography of the apices of first and second maxillary molars.

Materials and Methods

This in-vitro study was conducted on 35 permanent maxillary first and 35 permanent maxillary second molars collected from several dental clinics in Tehran. The teeth were stored in glass jars containing 10% formalin. The majority of teeth had been extracted due to periodontal problems and the remaining had small carious lesions or simple coronal restorations. The teeth that met the inclusion criteria underwent scaling and polishing and the soft tissue and bone residues and the calculi were removed. The access cavity was prepared using a diamond fissure bur (D & Z, Diamant, Germany) and high-speed handpiece (Kavo, West, Germany). Canal orifices were detected using the tip of DG16 endodontic explorer (Hu-Friedy, Chicago, IL, USA). The teeth were marked at the mesiobuccal line angle using a hand piece in an area close to the root without manipulating the root end using 0-1 system.  Next, the teeth were fixed and #8 K file (Kerr, SybronEndo, Germany) was inserted into the canals. The distance of the apical foramen from the anatomic apex and the amount and direction of deviation of the apical foramen from the anatomic apex mesiodistally and buccolingually were determined using a stereomicroscope (SZX ILLB200 Olympus Optical and LTD, Japan) under ×12 magnification and 0.01 mm readability. Specimens were immersed in 5.25% sodium hypochlorite solution (Golrang, Paakshou, Tehran, Iran) for 48h at room temperature (20°C) and then rinsed under running water for 4h.

In the next step, 2% methylene blue was injected via the access cavity into the canals using a 27 gauge insulin syringe (Supa, Tehran, Iran). Injection was done in two steps: while applying negative pressure at the apex using central suctioning system with an approximate pressure of 25 mmHg and then through the access cavity and without suctioning. Access cavity was then temporarily restored (Coltosol, Ariadent 37gr). The margins of the temporary restoration and tooth were coated with acrylic resin lacquer and the specimens were prepared for the process of decalcification and clearing.

For decalcification, the specimens were immersed in 5% nitric acid solution at room temperature for 3 days. The solution was stirred 3-4 times a day and refreshed daily. After 3 days, specimens were washed under running water for 4-6h. Dehydration was done using ethyl alcohol (Ararat, Tehran). Specimens were immersed in 80% ethyl alcohol for one day, 90% ethyl alcohol for an hour and 100% ethyl alcohol for another hour. Dehydrated teeth were cleared by immersion in methyl salicylate (Merck, Darmstadt, Germany) for 2h and evaluated and measured under stereomicroscopy at ×12 magnification and 0.01 mm readability. The morphology of the apical foramen was evaluated and the distance of the apical constriction from the center of the apical foramen and distance of the apical constriction from the anatomic apex were measured. Other morphological variations of the root canal system namely apical delta and type of canal according to Vertucci’s classification were also determined. The results were analyzed using sample t-test (P

Results

All maxillary first and second molars evaluated in our study had three roots and no separate extra root was found. MB, DB and palatal canals were present in all first and second molars but the MB2 canal was only observed in 12.5% and 40% of first and second molars, respectively. In this study, according to Vertucci’s classification, MB root canals in the maxillary first molar were type I and type IV in 87.5% and 12.5% of cases, respectively; and DB and P roots were type I in 100% of the cases. MB root in the maxillary second molar was type I in 60%, type II in 8.6%, type IV in 25.7% and type V in 5.7% of the cases (Figure 2). DB and P roots were type I in 100% of the cases (Table 1). The mean prevalence of apical delta (Figure 3) was 3.2% in the first and second maxillary molars.

Distance between apical foramen, apical constriction and anatomic apex in the canals of maxillary first and second molars is summarized in Table 2. In maxillary first molars, the distance from apical constriction to apical foramen was 0.21±0.09 mm, the distance from apical constriction to anatomic apex was 0.44± 0.19 mm and the distance from apical foramen to anatomic apex was 0.15±0.15mm.

Table 3 shows the prevalence (%) of deviation of apical foramina from the anatomic apex in the MB, DB and P canals of maxillary first and second molars (from the buccolingual and mesiodistal dimensions). The prevalence of non-deviated apical foramina from the mesiodistal and buccolingual dimensions in the MB1, MB2, DB and P canals of maxillary first molars was 15.6, 0, 3.1 and 25%, respectively. These values were 8.5, 14.2, 8.5 and 8.5 for the maxillary second molars, respectively.

Table 1. Prevalence of canal types based on Vertucci’s classification and prevalence of apical delta in the maxillary first and second molars in MB, DB and P roots

Table 2. Distance between apical foramen (AF), apical constriction (AC) and anatomic apex (AA) in MB, DB and P roots of the maxillary first and second molars(mm)

Table 3. Prevalence of apical foramen deviation from the anatomic apex in the maxillary first and second molars from the buccolingual (BL) and mesiodistal (MD) dimensions.